1. Field of the Invention
The present invention relates to a vehicular lamp having a discharge bulb suitable to serve as a vehicular headlamp. More particularly, the invention relates to a vehicular lamp which is capable of preventing an influence of electromagnetic waves of a lamp of the type having a discharge bulb as a light source thereof.
2. Related Art
In recent years, there has been investigated a lamp, particularly as a headlamp, having a discharge bulb which performs an excellent light emission efficiency and color rendering characteristic and exhibiting a long life. Since a lamp of the foregoing type however requires high voltage in order to actuate the discharge bulb to discharge electricity, a circuit for turning on the lamp is required to be attached to the lamp in order to raise the voltage of a battery mounted on the vehicle to a required level. The circuit for turning on the lamp involves high voltage being generated on the secondary side thereof, thus causing electromagnetic waves to be radiated outwardly. The electromagnetic waves, as noise, affect on electronic devices of the vehicle, thus resulting in normal operation of the electronic device being inhibited. For example, noise is generated in a radio and noise is unintentionally mixed with signal systems of computers mounted on the vehicle for performing a variety of controls. As a result, an undesirable phenomenon EMI (Electromagnetic Influence), takes place.
Further, since the circuit for turning on the lamp involves high voltage being generated on the secondary side thereof, it is required to shorten the secondary side wire as much as possible in view of the safety measurement. In this context, generally the turning-on circuit is installed integrally with the lamp body. On the other hand, in a case where the lamp body is designed to be compact, if the lamp is a headlamp which requires an optical axis adjustment mechanism for a reflector, the lamp body must have a space for allowing the movement of the optical axis adjustment mechanism to move within the lamp body. Accordingly, if the lamp body is designed to be compact, it is difficult to maintain a sufficient space for installing the turning-on circuit within the lamp body. Therefore, the turning-on circuit must be attached to the exterior of the lamp body. However, if the turning-on circuit must be attached to the exterior of the lamp body, the electromagnetic waves due to the high voltage generated by the turning-on circuit irradiate to the outside the lamp body. The electromagnetic waves generate noise which causes the afore-mentioned problems.
For this reason, the turning-on circuit is accommodated in a metal casing or the like having a shield effect to eliminate the irradiation of the electromagnetic waves. However, since a cord connecting the turning-on circuit to the discharge bulb extends to the outside the lamp body, the electromagnetic waves still irradiate from the connection code. It is not easy to avoid the irradiation of the electromagnetic waves. Further, the electromagnetic waves irradiate also from a connector portion of the connection code and the discharge bulb and also from the discharge bulb itself. It has been required to eliminates these extra irradiations of the electromagnetic waves.
Also electromagnetic waves of the above-mentioned type are generated in the discharge bulb to which the high voltage is applied. Electromagnetic waves generated by the discharge bulb cause the EMI to take place. Accordingly, a contrivance has been suggested in Unexamined Japanese Patent Publication No. Hei. 5-101703 which has a structure such that a shielding member for covering the discharge bulb is provided. The above-mentioned technique is structured to have the shielding member for inhibiting radiation of electromagnetic waves from the discharge bulb in order to prevent the EMI.
However, the above-mentioned conventional technique, which is effective in inhibiting radiation of electromagnetic waves from the discharge bulb, involves impossibility that the shielding member cannot be disposed in front of the discharge bulb, that is, in front of the lens of the lamp for outwardly emitting light generated by the discharge bulb. Therefore, electromagnetic waves radiated from the discharge bulb to positions in front of the head lamp cannot easily be shielded. As a result, electromagnetic waves radiated forward are reflected by the body of the head lamp or the body of the vehicle. Thus, reflection of the electromagnetic waves to the vehicle cannot be prevented and therefore the required effect of shielding electromagnetic waves cannot be obtained.